Gas concentrator with removable cartridge adsorbent beds

ABSTRACT

A portable oxygen concentrator designed for medical use where the adsorbent beds, are designed to be replaced by a patient. The concentrator is designed so that the power supply and adsorbent bed mount is one module and the compressor and air filter are part of another module configured to provide a unitary cooling and air supply system. Replacement beds may be installed easily by patients, and all gas seals will function properly after installation.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 120 as acontinuation of U.S. application Ser. No. 16/017,934, filed Jun. 25,2018, which is a continuation of U.S. application Ser. No. 14/142,613,filed on Dec. 27, 2013, now U.S. Pat. No. 10,004,869, each of which ishereby incorporated by reference in its entirety.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING

Not Applicable

BACKGROUND OF THE INVENTION

The invention generally relates to gas concentrators, and moreparticularly relates to medical oxygen concentrators used by patients inthe home care setting where cost and frequency of maintenance performedby a technician should be minimized.

The application of oxygen concentrators for therapeutic use is known,and many variants of such devices exist. A particularly useful class ofoxygen concentrators is designed to be used in a patient's home orworkplace without the assistance of a medical practitioner or caregiver.These home concentrators are typically referred to as stationaryconcentrators, as they are not designed to be carried by a patient,distinguishable from portable concentrators which are designed to becarried by a patient for most ambulatory activities. Most of theseoxygen concentrators are based on Pressure Swing Adsorption (PSA),Vacuum Pressure Swing Adsorption (VPSA), or Vacuum Swing Adsorption(VSA) designs which feed compressed air to selective adsorption beds,sometimes also referred to as sieve beds. In a typical oxygenconcentrator, the beds utilize a zeolite adsorbent to selectively adsorbnitrogen, resulting in pressurized, oxygen-rich product gas. This classof oxygen concentrator may also contain one or more systems to extendthe service life of the equipment. These systems may include softwarealgorithms to alter the PSA timing, input flow, or operating pressure toextend the performance of the adsorption beds as their capacity isreduced over its operating life as described in common inventors' priordisclosures U.S. Pat. No. 7,857,894 and its related applicationsincorporated in their entirety by reference. In these systems theadsorption beds may also include desiccant layers before the mainadsorbent layer to remove water and other contaminants or dedicatedwater removal components such as membrane air dryers as described incommon inventors' prior disclosures U.S. Pat. No. 7,780,768 and itsrelated applications, incorporated in their entirety by reference.

The main elements in a typical home-use therapeutic oxygen concentratorare shown in FIG. 1. Air is draw in, and typically filtered, at airinlet 1 before being pressurized by compressor 2 to a pressure of 1.2 to2.5 atmospheres. The pressurized air is directed by feed valvearrangement 9 through adsorbent beds 3. An exemplary adsorbent bedimplementation, used in a concentrator design developed by theinventors, is two columns filled with a lithium exchanged zeoliteadsorbent in the ratio of about 1 gram of adsorbent per 1-10 ml ofoxygen produced. The pressurized air is directed through these adsorberbed columns in a series of steps which constitute a gas separationcycle, often a PSA cycle or some variation including vacuum instead of,or in conjunction with, compression yielding overall compression ratiosof about 1.5:1 to 4.0:1. Although many different arrangements ofadsorber vessels and gas separation cycles are possible, the result isthat nitrogen is removed by the adsorbent material, and the resultingoxygen rich gas is routed 10 to a product gas storage device at 4. Someof the oxygen product gas can be routed back through the bed to flushout (purge) the adsorbed nitrogen to an exhaust 6. Generally multipleadsorbent beds, or columns in the exemplary device, are used so at leastone bed may be used to make product while at least one other bed isbeing purged, ensuring a continuous flow of product gas. The purged gasis exhausted from the concentrator at the exhaust 6.

Such gas separation systems are known in the art, and it is appreciatedthat the gas flow control through the compressor and the adsorbent bedsis complex and requires precise timing and control of parameters such aspressure, flow rate, and temperature to attain the desired oxygenconcentration of 80% to 95% purity in the product gas stream.Accordingly, most modern concentrators also have a programmablecontroller 5, typically a microprocessor, to monitor and control thevarious operating parameters of the gas separation cycle. In particular,the controller controls the timing and operation of the various valvesused to cycle the beds through feed, purge, and pressure equalizationsteps, which make up the gas separation cycle. Also present in oxygenconcentrators is an output control system 7 which acts to ensure thatthe therapeutic output flow of oxygen is continuous and steady evenduring the pressure swings associated with the production of the oxygen.A typical oxygen concentrator will also contain a user/data interface 8including elements such as an LCD display, alarm LEDs, audible buzzers,and control buttons. Portable oxygen concentrators would necessarilyalso include one or more battery packs for portable use.

To be conveniently used by an individual in a home or workplaceenvironment needing therapeutic oxygen, the stationary home oxygenconcentrators should be less than about 2100 cubic inches and preferablyless than 1600 cubic inches in total volume, less than about 25 poundsand preferably less than 20 pounds in weight, and produce less thanabout 45 decibels of audible noise, while retaining the capacity toproduce a flow of product gas adequate to provide for a patient's oxygenneeds, usually a flow rate prescribed by a medical practitioner in aboutthe range of 1 LPM to 5 LPM. Although stationary PSA based concentratorshave been available for many years, such fixed site units may weigh30-50 pounds or more, be several cubic feet in volume, and may producesound levels greater than 45 dBA. Thus they are loud and difficult tomove around. To achieve these beneficial improvements in noise andsize/weight, improved home oxygen concentrators involve a significantamount of miniaturization and efficiency improvements, leading tosmaller, more complex designs compared to older designs. System size,weight, and complexity may lead to fewer mitigative options or designchoices against contamination and other wear and tear effects that canlead to an unacceptably short maintenance interval, and thereforerequire novel design features to achieve both the improvements in sizeand noise while maintaining adequate lifetime.

It is therefore necessary to design home oxygen concentrators such thatzeolite contamination is handled in a manner that avoids costly orfrequent maintenance by a field technician or equipment provider. Theinventors have previously disclosed a system that achieves long sievebed life by removing water prior to the feed gas as described in theabove cited references. This approach may desirable for some portableoxygen concentrators where the beds are even smaller than a home basedstationary system, but because of the cost involved, may not beappropriate to stationary home based system where the price point needsto be very low. It is therefore desirable to design a home oxygenconcentrator that minimizes size and weight and cost as a function ofoxygen output with commonly available commercial adsorbents such asZ12-07 manufactured by Zeochem or Oxysiv MDX manufactured by UOP. Whileeliminating water removal components such as membrane air dryers orpretreatment layers such as activated alumina or a NaX type zeolite willreduce the cost of the adsorbent beds it will also reduce the servicelife of the beds to an unacceptable level. Oxygen equipment used forLong Term Oxygen Therapy (LTOT) is optimally deployed for 3-5 yearswithout any service requirements. Any service requirement within thattime interval simply adds to the overall cost of the equipment, whichsubstantially reverses any cost benefit gained by removing a membraneair dryer or pretreatment layer. Further, allowing sieve bedcontamination without prevention or service may lead to providing 82-87%purity oxygen instead of 87-95% pure oxygen to the patient. To reducethe overall cost of delivering oxygen therapy, devices must be designedthat do not require field service by a technician or equipment provider,and also minimize the cost, size, power consumption, and noise of theequipment that is used inside of the patient's home.

A typical adsorbent bed or adsorber is constructed of a column with aninlet port and an outlet port arranged at opposite ends. The adsorberswould typically be connected to the valve manifold of the concentratorthrough tubing or a direct manifold connection. Either prior artconstruction method resulted in a robust pneumatic connection that wasonly meant to be disconnected by a trained service technician who couldaccess the internal components of the concentrator and disconnect ordisassemble the inlet and outlet connections. Some columns, such asthose that are adhesive bonded to an integrated manifold, may not beremovable at all in a field service environment and must be replaced incombination with other system components to achieve zeolite replacement.Therefore user-replaceable adsorber beds are desirable and provide anapproach that may increase the service life of a concentrator withoutthe costly water removal components and without the need for factory orfactory trained service. Techniques for producing a medical concentratorof the portable type with user replaceable adsorber beds are describedin U.S. application Ser. Nos. 13/016,706 and 13/449,138 by commoninventors and incorporated in their entirety by reference

BRIEF SUMMARY OF THE INVENTION

The invention is an improved stationary home oxygen concentrator,including a PSA/VPSA/VSA core section capable of mating with userreplaceable adsorbers, the core section including:

-   -   a housing    -   a controller    -   a user interface    -   at least two user replaceable adsorber beds    -   at least one compressor, air control valve, and air filter,        making a PSA/VPSA/VSA oxygen system when mated with the user        replaceable adsorbers    -   a patient delivery apparatus        The concentrator also includes a module of at least one AC-DC        power supply and docking elements for the user replaceable beds.        The concentrator includes another module including the        compressor and an air blower. The blower, and air inlets and        outlets are arranged to form a unitary cooling and acoustic        damping air flow system drawing air in from one side of the        housing over the beds and over the compressor and power supply        while directing exhaust gas from the beds to the muffler and        both exhaust and cooling air directed out of the housing on an        opposite side from the inlet.

Preferably, the concentrator weighs less than 25 pounds, produces lessthan 50 dba acoustic noise when operating, and has an output gas flow of5 lpm or less.

In some embodiments, the concentrator has an input to receive the outputfrom an external rechargeable battery capable of running theconcentrator for greater than 2 hours. The concentrator may in theseembodiments be switched between operating from the internal AC-DC powersupply and the external battery. The adsorbers and the power supplymodule may be enclosed in a lower housing component that has rubbervibration and noise isolating feet or wheels.

In other embodiments the DC power input may also include a communicationbus to communicate state and power information to the microprocessor onthe concentrator. The concentrator in some embodiments may also includea diagnostics interface.

In some embodiments, an inlet filter is mounted to the exterior of theconcentrator (which may form an ornamental surface of the exterior). Theinlet filter may also form a portion of a mount for a humidifier. Theinlet to the inlet filter is preferably directed into the interior ofthe concentrator to reduce external noise sources and source air fromfiltered air that has passed through the gross particle filter.Preferably the chassis directs airflow over at least the compressor andthe power supply and the inlet cooling air is directed over theadsorbent beds.

In some embodiments the compressor subchassis is interconnected to thechassis via rails to provide a high amount of surface engagement todistribute shock load and prevent breakage of the chassis.

In some embodiments, the intake silencer and exhaust muffler are acommon structure. Preferably, the lower housing cover may be removed toaccess the replaceable adsorber beds

In additional embodiments the detachable lower housing may be equippedwith either rubber vibration isolation feet or wheels to increase easeof movement within a house and best fit a patient's mode of usage forthe equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The understanding of the following detailed description of certainpreferred embodiments of the invention will be facilitated by referringto the accompanying figures.

FIG. 1 shows the general elements of gas concentrators as applicable tocertain embodiments of the invention.

FIG. 2 illustrates the general concept where the concentrator platformis one portion and the user replaceable adsorber is another portion thattogether form a complete portable oxygen concentrator.

FIG. 3 shows an exemplary external layout of the concentrator.

FIG. 4 illustrates an exemplary modular design of the concentrator.

FIG. 5 illustrates additional exemplary elements of the concentrator.

FIG. 6 depicts the novel open airflow design of the concentrator.

FIG. 7 illustrates the novel air connection design of the concentrator.

FIG. 8 depicts a protective covering for the power supply/bed module.

FIG. 9 depicts an exemplary view of the external power supply input, airfilter, and diagnostics port of the concentrator.

DETAILED DESCRIPTION OF THE INVENTION

An ideal home stationary concentrator should still be light and compactenough for ease of movement and placement for use by a patient asopposed to a technician or caregiver. This class of equipment shouldpreferably operate reliably for many years without the need forprofessional service and maintenance. These improved home oxygenconcentrators are typically in the range of 10 to 20 lbs and producefrom 0.3 to 5.0 LPM of oxygen. A particularly effective embodiment ofthe invention is an oxygen concentrator where the sieve bed cartridgesor adsorbers can be removed and replaced without removing any fastenersor exposing internal operating components. FIG. 2 illustrates anembodiment of an exemplary concentrator suitable for the invention. Oneskilled in the art will appreciate that the alterations of designelements and arrangement of components from the exemplary design shownare possible to practice the novel elements of the invention. Thus theexemplary design shown is not limiting and the invention is limited onlyby the claims. The novel stationary concentrator incorporates multipleelements distinct from the portable concentrator with user replaceablebeds described in application Ser. No. 13/016,706, but also benefitsfrom a replaceable bed design. As shown in FIG. 2 beds 21 interface tothe other concentrator components 20 through feed gas connections 201and 211, product gas connections 212 and 202 and are secured withretention mechanisms 213 and 203, examples of which are disclosed inapplication Ser. No. 13/016,706. The novel stationary concentrator hasadditional elements modularly attached to the core control andcompressor section of the concentrator. The filter and power supply arelocated on the outside of the core structure while the adsorbent bedsare internal to the outer casing to provide additional forced coolingair to pass over the adsorbent beds. The product gas connection 202 foreach adsorber has been joined into a common element to reduce partcount. Feed gas connections 201 and mating element 203 have also beenintegrated into a single element to reduce part count. A compressorinlet silencer 130 is added to the airflow system and the whole airintake/cooling system is a unitary design that achieves multipleobjectives with a relatively small number of elements. In addition thenovel stationary concentrator preferably operates with a power supply 17which can be plugged into an AC power source (wall power) as well asoptionally operating off of DC power 18, such as an external batterypack 18. The DC power option is particularly useful if the user'sambulatory needs include wheeled appliances such as walkers orwheelchairs, which can easily transport a concentrator in the size rangeenvisioned, thus adding an element of portability to the novelstationary concentrator.

Referring to FIG. 3, some exterior elements of an exemplary concentrator100 are shown. The outer housing panels include a front and rear panel,13 and 12, control panel 16 with an optional mount 11 for an externalhumidifier. Also shown are an intake panel 14, containing the grossparticle filter 1 and exhaust panel 15 and a lower housing 101. In theexemplary concentrator design front 13 and rear 12 panels are removableby hidden screws that can be located when lower housing 101 is removed.The lower housing can be removed without tools to access the removableadsorbers. Lower, front, and rear panels can be removed during operationof the concentrator for easy service and troubleshooting. The front 13and rear 12 panels are removable in such a way that they are the lastelements of installation before the lower housing. Removing them exposesthe internals of the concentrator while the intake housing 14 and theexhaust housing 15 continue to support the control panel housing 16.This exemplary arrangement is beneficial for repair and troubleshooting.

FIG. 4 illustrates internal elements of the novel concentrator. Theconcentrator includes two modules, the compressor module 120 and thePower supply/bed dock module 110. Blower 140 is part of the compressormodule 120 as are silencing elements exhaust muffler 130 and compressorintake silencer 131. Since the predominance of the noise from theconcentrator originates at the compressor intake, the intake silencer islocated between the compressor and the externally mounted air filter toprevent noise being communicated to the exterior of the concentrator.The muffler likewise must handle the large volume of gas generated whenan adsorber is exhausted. This exhaust gas is routed into the compressorchassis to maximally contain the exhaust sound and to prevent thenitrogen rich exhaust gas from being recycled into the compressorintake. Referring to FIG. 5, the compressor is mounted to a modular loaddispersing element 121 to prevent chassis damage during shipment. Thisstructure has a high surface area interface to the chassis and preventsthe fasteners from being load concentrating elements by utilizing asliding rail system to retain the structure in multiple orientations.The load dispersing element 121 also contains cooling ducts 123 from thecompressor module to the power supply module to ensure the cooling fanis actively cooling the power supply. The compressor module containsexhaust gas ducting 124 to the muffler as well as compressor coolingducting 122. The power supply/bed dock module 110 contains the adsorberalignment guides 112, adsorber retention latches 113 and the lowerhousing (boot) latches 111. The bed retention system may be one ofseveral forms, such as those described in application Ser. No.13/016,706

FIGS. 6 and 7 illustrate the unitary cooling/acoustic damping airflowsystem of the concentrator 100. FIG. 6 illustrates the open flow portionof the air system. Blower 140 intakes air from the intake gross particlefilter 14 in a tortuous path over the adsorbent beds 160. This air pathensures that the adsorbent beds are cooled with the coolest possible airand that the heat generated from the compressor 180 and power supply 190is not directed back to other components in the system. The blowerdischarge air is directed over the compressor heads and cylinders 16which are the most temperature sensitive parts of the system. Thecooling air then passes over the compressor 180 motor and power supply190 before being expelled out the exhaust to minimize the heat build upin the system and minimize the escaping noise through the vents. Thisprogressive cooling system ensures that the sensitivity of the componentto heat is commensurate with its location in the cooling air path. Thecooling layout is also optimized to ensure that heat buildup occurs nearthe exhaust exit to minimize heat retention in the system and thermalheating of non-heat generating components such as the valves and circuitboard.

The concentrator 100 piped airflow portion is shown in FIG. 7. Intakeconnection 171 collects ambient air as it is drawn in through the grossparticle filter and air inlet 160 and draws it into the compressor airfilter 174. The intake air is routed to intake silencer 131 from thecompressor air filter whose output is routed to the compressor bycompressor connector 172. Bed product gas is routed toward patient byconnection 173, while exhaust gas is routed to muffler 130 by connection170. Muffler output is vented 123 to the compressor module as shown inFIG. 5 location 124. Where it is pushed to the panel outlet by the openairflow through the compressor module 120. Thus the blower is the singlepoint of origin for the unitary air system, which includes silencingelements for both compressor input and exhaust output, as well ascomprehensive cooling and exhaust gas management.

FIG. 8 illustrates an embodiment which may include a removableprotective boot 150 which fits over the bottom panel 101. This bootpreferably is easily removable, by the user, and when removed providesaccess to the beds and bed retention mechanisms. Thus the beds may beremoved and replaced simply by removing the boot with no otherdisassembly required. The boot may optionally include isolation feetand/or wheels. As was shown in FIG. 5 the adsorber and power supplysubchassis 110 houses the power supply and the adsorber mounting, two ofthe critical components of the oxygen concentrator covered by lowerhousing component 101. To ensure that these components are protectedfrom external damage or contamination from water and debris, the lowerhousing component 101 in FIG. 8 is a snap on cover that offersprotection to the internal components of the power supply and adsorbersubchassis. Optional rubber isolation feet 102 are depicted in FIG. 3 toensure that the vibration and noise from the concentrator are notrigidly coupled to the floor or other operating surface of theconcentrator. The removable lower housing can be removed by the user toaccess and change the adsorbent beds. Therefore, the removal of thelower housing without tools is important to allow the user to change theadsorbent beds rather than a technician or service provider.

FIG. 9 illustrates how the preferred embodiment of the improvedstationary concentrator includes the adaptability of an alternate powerinput port 90 designed to operate the system on DC input power. The DCpower may be supplied by an external battery system or other DC powersource such as a vehicle. In this preferred embodiment, the power inputconnector includes at least one communication line to facilitateidentification of the type and configuration of the DC power source.This is the preferred embodiment because it allows for flexible powermoding such that the concentrator may restrict its allowed flow settingsto match the available power of the DC power source. For example, astandard automobile power outlet may supply only 120 W and theconcentrator may limit operation to 3 LPM or less to prevent malfunctionor damage to the DC power source. Whereas the presence of a largerexternal battery or power supply may allow full range operation and theinformation communicated between the power source and the concentrator'sDC input system can allow for this optimized operation.

In another embodiment of the improved stationary concentrator, there isa diagnostic interface 92 located on the rear panel of the concentratoras seen in FIG. 9. This connector serves a range of purposes that mayinclude providing a display output to show additional information aboutthe internal operating conditions of the concentrator. The diagnosticconnector may also include other functionality such as a USB interfaceor software update port that was previously a discreet output onportable oxygen concentrators where cost is less of a concern. Thisdiagnostic port connector allows for cost to be removed from the hostconcentrator system and moved to a diagnostic interface system such thatthe cost is not incurred on every concentrator.

The preferred embodiment depicted in FIG. 9 additionally includes anexternally mounted air intake filter 91 that feeds air into thecompressor. The topside external location of this filter allows easyaccess by the user to check the dirt loading of the filter and toreplace the filter as needed without the assistance of a technician orservice provider. Unlike other stationary concentrators that locate thefilter behind a trap door, the filter 91 depicted in FIG. 9 does notrequire any opening of the concentrator for access. The filter furtherincludes a clear housing component that allows direct visual evaluationof the filter element by the user so that the replacement of the filtercan be limited by need rather than specified at discrete orpredetermined intervals of time or run hours. The topside location alsoallows ease of access to the user so that the user does not have tokneel down of lift the concentrator up to access the filter forinspection or replacement. In a preferred embodiment the air filter mayform an ornamental portion of the concentrator case and my includefeatures such as slots 93 to mount the humidifier accessory to theconcentrator. This mounting location ensures the filter is located in acommonly accessed location. This specific configuration also ensuresthat any damage to the humidifier mount can be replaced by replacing theuser replaceable intake filter thus avoiding a repair by a technician orservice provider.

The inlet filter depicted in FIG. 9 is directed to intake ambient airinto the compressor system from the intake side of the air blower. Thisoptimal configuration ensures that the compressor receives cool ambientair that is free from concentrated nitrogen because the exhaust gas isdirected into the exhaust side chamber of the air blower. The air inletconfiguration depicted in FIG. 9 further contributes to low noiseoperation because the intake filter ports 94 are directed into theinterior of the concentrator so that the intake valve noise from thecompressor that escapes back through the filter element and housing isnot directed to the exterior of the concentrator where it would be moreaudible to the user.

In an optional configuration, the lower housing 101 depicted in FIG. 3can also be modified to meet specific user needs and can be easilyswapped during any stage of manufacturing or deployment of theconcentrator since the lower housing can be removed and replaced withouttools. For example, the rubber vibration isolation feet 102 can besubstituted for caster wheels or a battery cart mounting system inalternate configurations. The changeable lower housing serves to allowthe concentrator to serve a multitude of purposes as well as providingfor easy replacement in the case of damage. A common failure mode orprior art stationary concentrator is the caster wheels being brokenduring shipping, transport or usage. When these caster wheels arebroken, the entire housing must be replaced since the housings aretypically composed of large clamshell type enclosures or intricate lowerhousings that are integrated to such other components such as compressormounts or internal chassis. The separate and simple lower housing in theinvention further simplifies service, configuration, and maintenance ofthe concentrator while in service and reduces the need to remove theconcentrator from service to perform repairs.

The foregoing description of the preferred embodiments of the presentinvention has shown, described and pointed out the fundamental novelfeatures of the invention. It will be understood that various omissions,substitutions, and changes in the form of the detail of the apparatus asillustrated as well as the uses thereof, may be made by those skilled inthe art, without departing from the spirit of the invention.Consequently, the scope of the invention should not be limited to theforegoing discussions, but should be defined by appended claims.

1. (canceled)
 2. A portable oxygen concentrator platform, comprising:one of a PSA, VPSA or VSA core section comprising: a housing; acontroller; a user interface; at least two adsorber beds; at least onecompressor; an airblower; a power supply module comprising at least onepower supply; and a compressor module comprising the compressor and acompressor mount, wherein the power supply module and the compressormodule are configured to mate together, and when mated the combinedmodules and housing are configured to form a unitary cooling andacoustic damping air flow system and to direct cooling air over at leastthe adsorbent beds, the compressor, and the power supply; and whereinthe portable oxygen concentrator weighs less than 25 pounds, producesless than 50 dBA acoustic noise when operating, and has an output gasflow of 5 lpm or less.
 3. The concentrator of claim 2, furthercomprising an input to receive an output from an external rechargeablebattery capable of running the concentrator for greater than 2 hours. 4.The concentrator of claim 3, wherein the concentrator may be switchedbetween operating from the internal power supply and the externalbattery.
 5. The concentrator of claim 2, further comprising a compressorinlet filter mounted to an exterior of the concentrator.
 6. Theconcentrator of claim 5, further comprising an air filter, wherein aninlet and an outlet of the air filter are connected to an interior ofthe concentrator.
 7. The concentrator of claim 5, wherein the compressorinlet filter forms an ornamental surface of the exterior.
 8. Theconcentrator of claim 5, wherein the compressor inlet filter forms aportion of a humidifier mount.
 9. The concentrator of claim 2, whereinthe compressor module is interconnected to the power supply module viarails to provide a high amount of surface engagement to distribute shockload and prevent breakage of a chassis.
 10. The concentrator of claim 2,wherein the power supply module is configured to mate to a removablelower housing component comprising at least one of rubber vibration andnoise isolating feet or wheels.
 11. The concentrator of claim 2, furthercomprising an intake silencer, wherein the intake silencer and anexhaust muffler are a common structure.
 12. The concentrator of claim 2,further comprising a diagnostics interface.
 13. The concentrator ofclaim 12 wherein the diagnostics interface is externally accessible. 14.The concentrator of claim 13 wherein the diagnostics interface mates toan external readout when the concentrator is serviced.